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/*

 * Copyright © 2012 Vincent Lejeune

 * Copyright © 2012 Intel Corporation

 *

 * Permission is hereby granted, free of charge, to any person obtaining a

 * copy of this software and associated documentation files (the "Software"),

 * to deal in the Software without restriction, including without limitation

 * the rights to use, copy, modify, merge, publish, distribute, sublicense,

 * and/or sell copies of the Software, and to permit persons to whom the

 * Software is furnished to do so, subject to the following conditions:

 *

 * The above copyright notice and this permission notice (including the next

 * paragraph) shall be included in all copies or substantial portions of the

 * Software.

 *

 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR

 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,

 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL

 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER

 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING

 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER

 * DEALINGS IN THE SOFTWARE.

 */

#include "ir.h"

#include "program/hash_table.h"

/**

 * \file lower_output_reads.cpp

 *

 * In GLSL, shader output variables (such as varyings) can be both read and

 * written.  However, on some hardware, reading an output register causes

 * trouble.

 *

 * This pass creates temporary shadow copies of every (used) shader output,

 * and replaces all accesses to use those instead.  It also adds code to the

 * main() function to copy the final values to the actual shader outputs.

 */

namespace {

class output_read_remover : public ir_hierarchical_visitor {

protected:

   /**

    * A hash table mapping from the original ir_variable shader outputs

    * (ir_var_shader_out mode) to the new temporaries to be used instead.

    */

   hash_table *replacements;

   void *mem_ctx;

public:

   output_read_remover();

   ~output_read_remover();

   virtual ir_visitor_status visit(class ir_dereference_variable *);

   virtual ir_visitor_status visit_leave(class ir_emit_vertex *);

   virtual ir_visitor_status visit_leave(class ir_return *);

   virtual ir_visitor_status visit_leave(class ir_function_signature *);

};

} /* anonymous namespace */

/**

 * Hash function for the output variables - computes the hash of the name.

 * NOTE: We're using the name string to ensure that the hash doesn't depend

 * on any random factors, otherwise the output_read_remover could produce

 * the random order of the assignments.

 *

 * NOTE: If you want to reuse this function please take into account that

 * generally the names of the variables are non-unique.

 */

static unsigned

hash_table_var_hash(const void *key)

{

   const ir_variable * var = static_cast(key);

   return hash_table_string_hash(var->name);

}

output_read_remover::output_read_remover()

{

   mem_ctx = ralloc_context(NULL);

   replacements =

      hash_table_ctor(0, hash_table_var_hash, hash_table_pointer_compare);

}

output_read_remover::~output_read_remover()

{

   hash_table_dtor(replacements);

   ralloc_free(mem_ctx);

}

ir_visitor_status

output_read_remover::visit(ir_dereference_variable *ir)

{

   if (ir->var->data.mode != ir_var_shader_out)

      return visit_continue;

   ir_variable *temp = (ir_variable *) hash_table_find(replacements, ir->var);

   /* If we don't have an existing temporary, create one. */

   if (temp == NULL) {

      void *var_ctx = ralloc_parent(ir->var);

      temp = new(var_ctx) ir_variable(ir->var->type, ir->var->name,

                                      ir_var_temporary);

      hash_table_insert(replacements, temp, ir->var);

      ir->var->insert_after(temp);

   }

   /* Update the dereference to use the temporary */

   ir->var = temp;

   return visit_continue;

}

/**

 * Create an assignment to copy a temporary value back to the actual output.

 */

static ir_assignment *

copy(void *ctx, ir_variable *output, ir_variable *temp)

{

   ir_dereference_variable *lhs = new(ctx) ir_dereference_variable(output);

   ir_dereference_variable *rhs = new(ctx) ir_dereference_variable(temp);

   return new(ctx) ir_assignment(lhs, rhs);

}

/** Insert a copy-back assignment before a "return" statement or a call to

 * EmitVertex().

 */

static void

emit_return_copy(const void *key, void *data, void *closure)

{

   ir_return *ir = (ir_return *) closure;

   ir->insert_before(copy(ir, (ir_variable *) key, (ir_variable *) data));

}

/** Insert a copy-back assignment at the end of the main() function */

static void

emit_main_copy(const void *key, void *data, void *closure)

{

   ir_function_signature *sig = (ir_function_signature *) closure;

   sig->body.push_tail(copy(sig, (ir_variable *) key, (ir_variable *) data));

}

ir_visitor_status

output_read_remover::visit_leave(ir_return *ir)

{

   hash_table_call_foreach(replacements, emit_return_copy, ir);

   return visit_continue;

}

ir_visitor_status

output_read_remover::visit_leave(ir_emit_vertex *ir)

{

   hash_table_call_foreach(replacements, emit_return_copy, ir);

   hash_table_clear(replacements);

   return visit_continue;

}

ir_visitor_status

output_read_remover::visit_leave(ir_function_signature *sig)

{

   if (strcmp(sig->function_name(), "main") != 0)

      return visit_continue;

   hash_table_call_foreach(replacements, emit_main_copy, sig);

   return visit_continue;

}

void

lower_output_reads(exec_list *instructions)

{

   output_read_remover v;

   visit_list_elements(&v, instructions);

}